Cleanup agents



Patented Aug. 26, 1941 UNITED CLEANUP AGENTS John D. McQuade, Lakewood,Ohio, assignor to Kemet Laboratories Company, Inc., a corporation of NewYork No Drawing. Application February 15, 1938, Serial No. 190,583

4 Claims.

This invention relates to clean-up agents used in producing a highvacuum. More particularly, it refers to improvements in clean-up agentsof the type employed in the manufacture of thermionic valves such asradio tubes.

High vacua are commonly produced in radio tubes by pumping most of thegas out of the envelope of the tube and subsequently increasing thevacuum thus obtained by vaporizing or flashing within the envelope ahighly reactive substance or getter material which adsorbs withconsiderable force, and if the envelope is made of glass, the impactbetween these hot particles and the relatively cold glass may cause thelatter to crack. Moreover, loose metallic particles within the tubeinterfere with its proper performance.

Attempts have been made to prevent the escape of such metallic particlesfrom the flashed getter material by covering the getter tablet withscreens or shields of various designs, but no completely eiiectivedevice of this kind has been developed.

The principal object of the present invention is to avoid thesedisadvantages which are inherent in getter materials of the kinddescribed. This object is attained by providing a new and improvedgetter material which when flashed vaporizes smoothly and withoutsputtering.

In 'its general aspect, the invention comprises an active gettermaterial in admixture with an effective amount of a comminutedrefractory material which is relatively inert under flashing conditions,will not react to a substantial extent with the active getter materialand is relatively nonvolatile at flashing temperatures, ranging usuallybetween 850 and 1150 C. Substances suitable for this purpose includerefractory oxides and refractory metals such as alumina, silica,magnesia, molybdenum, or tungsten or mixtures thereof. Among these,alumina is the most effective.

The amount of the refractory material preferably is between 3% and 20%of the total weight of the mixture. Within this percentage range, theoptimum. quantity of refractory material depends on its composition aswell as on the kind of active getter material. For example, an additionof about 7% by weight of alumina was found to give best results with anactive getter material consisting of a barium-aluminummagnesium alloy,while an addition of about 10% by weight of alumina is best when usingan active getter material consisting of an alloy of barium and magnesiumonly.

The refractory material preferably is finely powdered and thoroughlymixed with powdered active material and the mixture may bepressed toform tablets or pills. These may then be embedded or otherwise attachedto a getter tab or other suitable holder.

Extensive experiments have shown that the violence of vaporization ofthe getter material is appreciably decreased and that the deleteriousejection of metallic particles is avoided.

I claim:

1. Clean-up agents, for thermionic valves, composed of comminuted activegetter alloy of barium and magnesium and from 7% to 15% by weight of atleast one comminuted refractory oxide selected from the group consistingof alumina, silica, and magnesia which under flashing conditions issubstantially inert and non-volatile.

2. Clean-up agents, for thermionic valves, composed of comminuted activegetter alloy of barium and magnesium and from 7% to 15% by weight ofcomminuted alumina.

3. Clean-up agents, for thermionic valves, composed of comminuted activegetter alloy of. barium and magnesium and from 7% to 15% by weight ofcomminuted silica.

l. Clean-up agents, for thermionic valves,

composed of comminuted active getter alloy of barium and magnesium andfrom 7% to 15%by weight of comminuted magnesia.

JOHN D. MCQUADE.

